Galvanomagnetic resistance device

ABSTRACT

A permanent magnet has a length which is small compared to its cross-section. The yoke of the magnetic biasing circuit is in direct contact with one narrow side of the magnet. The control flux phi s and the bias flux phi v are decoupled from each other by magnetic saturation of the pole piece which is not adjacent to the field plate. The resultant galvanomagnetic resistance device has a sensitivity which is so great that even stray fields may be detected.

United States Patent [191 Hini et al.

[ Oct. 9, 1973 GALVANOMAGNETIC RESISTANCE DEVICE Inventors: Paul Hini; Adolf Albrecht, both of Erlangen, Germany Assignee: Siemens Aktiengesellschaft, Berlin &

Munchen, Germany Filed: Aug. 18, 1971 Appl. No.: 172,782

Foreign Application Priority Data Aug. 27, 1970 Germany P 20 42 491.5

[1.8. CI 338/32 R Int. Cl H01c 7/16 Field of Search 338/32 R, 32 H;

[56] References Cited UNITED STATES PATENTS 3,537,046 10/1970 l-lubrich et a1. 338/32 R Primary ExaminerC. L. Albritton AttorneyArthur E. Wilfond et a1.

[5 7] ABSTRACT A permanent magnet has a length which is small compared to its cross-section. The yoke of the magnetic biasing circuit is in direct contact with one narrow side of the magnet. The control flux d), and the bias flux (b, are decoupled from each other by magnetic saturation of the pole piece which is not adjacent to the field plate. The resultant galvanomagnetic resistance device has a sensitivity which is so great that even stray fields may be detected.

25 Claims, 9 Drawing Figures GALVANOMAGNETIC RESISTANCE DEVICE The invention relates to a galvanomagnetic resistance device. More particularly, the invention relates to a magnetic field-dependent resistance device having a magnetic circuit which includes a permanent magnet of low permeability and ferromagnetic pole pieces which are in contact with the poles and are connected to each other via the yoke of the magnetic circuit and via a field plate which functions as the magnetic fielddependent resistance.

The textbook entitled The Physics and Application of Galvanomagnetic Devices by Weiss, Vieweg Verlag, 1969, page 327, and the English translation, Pergamon Press, 1969, page 322, describes a probe for position finding by means of magnetic field-dependent semiconductor resistors which are hereinafter called field plates. Two U-shaped ferrite parts form a rectangularly shaped magnetic circuit having two air gaps, each of which contains a field plate. The ferrite parts are cemented to a'ferromagnetic support to keep the effective air gap small. Two windings are provided on the two legs of the iron circuit and supply a biasing magnetic induction for the field plates. The change in the bias of the field plates by an external control field is a measure of the magnitude of such control field.

On page 331 of the aforedescribed textbook and page 326 of the English translation thereof, a resistor arrangement is described. The resistor arrangement has a single biased field plate in the air gap of the biasing circuit. The pole pieces of the biasing circuit are designed as collector plates for the control field. The collector plates or magnetic sensing antennae comprise extensions of the pole pieces and extend in directions parallel to the axis of the magnet. The sensing antennae permit even a weak magnetic fiux of the control field to be captured and concentrated onto the field plate. A sufficiently strong magnetic induction is thereby obtained for controlling the resistance of the fieldplate.

The periodical Elektronik, 1965, No. 8, pages 228 and 229, discloses a resistance device for sensing the magnitude and polarity of magnetic fields by two biased field plates which are penetrated by the fields of two permanent magnets connected in series in the magnetic circuit. The field plates are connected in the opposite sense in different branches of a bridge circuit. The external control field is subtracted from the bias field in one field plate and added to the biasfield in the other field plate. The external control field therefore changes the resistance of the field plates.

In the disclosure of the German Provisional Pat. No. 1,302,746, the resistance arrangement for sensing the magnitude and polarization of external magnetic fields is simplified and improved by a single block-shaped permanent magnet which is preferably an oxide magnet of small permeability. The pole pieces adjoining the pole ends of the magnet are aligned approximately perpendicularly to the external magnetic field and protrude on one side. The field plate is inserted in a ferromagnetic or ferrite mounting at the ends of the pole piece facing away from the permanent magnet. The part of the biasing circuit containing the magnet therefore has a high magnetic resistance and the part containing the field plate has a low magnetic resistance. For this reason, a substantial part of the magnetic flux is concentrated in the field plate.

An object of the invention is to provide a galvanomagnetic resistance device having a sensitivity which is greater than that of known similar devices.

Another object of the invention is to provide a galvanomagnetic resistance device having such great sensitivity that it detects even stray fields. I 1

Still another object of our invention is to provide a galvanomagnetic resistance device which prevents the formation of substantial stray fields in the area of the magnetic yoke.

Another object of the invention is to provide a galvanomagnetic resistance device which is of simple structure, but functions with efficiency, effectiveness and reliability.

Our invention is based upon the recognition that the concentrating effect of the magnetic yoke, and thereby the sensitivity of the arrangement, may substantially be increased further if the volume of the magnet is brought as close as possible to the air gap containing the field plate.

In accordance with our invention, the aforedescribed problem is solved by placing the magnetic yoke in contact, without appreciable spacing, with one narrow side of the permanent magnet. The length of the permanent magnet is small in the direction of its magnetic axis, as

compared to its cross-section. The control field penetrates the yoke and the pole piece. One end of the pole piece provides the boundary of the air gap containing the field plate. In the aforedescribed resistance arrangement, a substantial portion of the stray flux is also concentrated in the magnetic yoke and therefore in the field plate, and is picked up as usable flux. The yoke connects the end of the pole piece to the end of a second pole piece via the field plate. Thus, an important feature of the galvanomagnetic resistance device of the invention is that the volume of the permanent magnet, and therefore its energy, isshifted directly to the field plate. This prevents the formation of substantial stray fields in the area of the magnetic yoke.

The field plate may be positioned in a simple manner on one flat side of the magnetic yoke which may also serve as the base plate of the galvanomagnetic resistance device. The field plate may also be directly affixed to the end face of one of the pole pieces. The field plate must, of course, be insulated from the electrically conductive parts of the biasing circuit. In any event, the field plate may be directly affixed, without special support and without special mounting, to a body adjoining the air gap. Such field plates may be manufactured in accordance with the method disclosed in U. S. Pat. No. 3,534,467. When such a field plate is utilized, the length of the air gap is substantially determined by the very small thickness of said field plate.

Another feature of the galvanomagnetic resistance device of the invention is that, in orderto decouple the control flux and the bias flux, a part of the permanent magnet circuit, which is not penetrated by the control field, is given an increased magnetic resistance, which exclusively affects the control field. The effect on the control field is achieved by the provision that this part of the circuit is already saturated, at least approximately, by the biasing field of the permanent magnet. A high resistance for the control field and a corresponding displacement of the control field to the part of the magnetic circuit containing the field plate are thereby obtained.

Still another improvement provided by the galvanomagnetic resistance device of the invention is attained by reducing the stray field of the pole pieces on the narrow sides of the magnet which are not in contact with the yoke. The improvement is obtained by extending the magnet beyond the pole pieces or by correspondingly shortening the two polepieces. The field of the part of the permanent magnet which protrudes beyond the pole pieces then counteracts the stray field of the pole pieces.

The galvanomagnetic resistance device of our invention may be further improved by providing collector plates for the control field. The collector plates function as magnetic antennae and may increase the induction in the air gap considerably by capturing a substantial part of the stray field. At least one of the collector plates in each instance may advantageously be bent at an angle. One leg of such collector plate is then in contact with one of the pole pieces or with the magnetic yoke and functions as the distributor for the control field. The free leg of such collector plate, which is preferably substantially longer, is directed away from the arrangement at least approximately in the direction of the control field. If the stray field is directed approximately perpendicularly to the magnetic axis of the permanent magnet, it is advantageous that the collector plate adjoining the magnetic yoke be bent, whereas for picking up an external field extending in the direction of the permanent magnet, the collector plate adjoining the pole piece is an angle plate.

Another, particularly advantageous, embodiment of the galvanomagnetic resistance device of the invention is provided by shaping both collector plates as angle plates. If one of the collector plates is in contact with a pole piece, which is preferably the pole piece engaging the field plate, and the other collector plate is in contact with the magnetic yoke, the free legs are approximately'in the direction of the external field. If an approximately homogeneous field is to be picked up, the free legs are in approximately opposite directions and thereby form an angle of about 180. However, a curved field may also be picked up. In such case, the free legs form an angle which is preferably smaller than 180 and may also be approximately 90.

The galvanomagnetic resistance device of the invention is highly suitable for sensing a curved control field having lines of force, for example, which enter one of the pole pieces approximately perpendicularly, penetrate the field plate, and then leave the magnetic yoke, or vice versa, as is the case even when there are no collector plates. The curved fields are additionally concentrated in the field plate by the collector plate of the aforedescribed embodiment. Thus, the aforedescribed embodiment increases the sensitivity of the galvanomagnetic resistance device of the invention to the extent that it is able to detect stray fields of the order of a few millitesla such as, for example, to millitesla. A Tesla or T is equal to 10 Gauss.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein:

. FIG. 1 is a schematic diagram of an embodiment of the galvanomagnetic resistance device of the invention, showing the pattern of the magnetic fluxes;

FIG. 2 is a schematic diagram of another embodiment of the galvanomagnetic resistance device of the invention utilizing a specific embodiment of a magnetic yoke;

FIG. 3 is a schematic diagram of a portion of the embodiment of FIG. 2 illustrating the field pattern at the end of the permanent magnet opposite the magnetic yoke;

FIG. 4 is a perspective view of an embodiment of the galvanomagnetic resistance device of the invention;

FIG. 5 is a perspective view of still another embodiment of the galvanomagnetic resistance device of the invention utilizing a specific biasing circuit; and

FIGS. 6a, 6b, 6c and 6d are schematic diagrams illustrating different modifications of the positions of the collector plates or magnetic sensing antennae of the galvanomagnetic resistance deviceof the invention.

In the FIGS., the same components are identified by the same reference numerals.

In FIG. 1, a permanent magnet 2 comprises a slab magnet having narrow faces which are substantially smaller than the area of the flat sides thereof. The flat sides of the permanent magnet may function as pole faces, as indicated by N and S. A pole piece 4 is in contact with the pole face S and a pole piece 6 is in contact with the pole piece N of the permanent magnet 2.

The pole pieces 4 and 6 comprise ferromagnetic material or ferrite. One end of each of the pole pieces 4 and 6 is connected to that of the other via a magnetic yoke 8 and a field plate 10 which functions as the magnetic field-dependent resistance. The magnetic yoke 8 comprises ferromagnetic material or ferrite and preferably contacts a narrow face of the permanent magnet 2. The magnetic yoke 8 may be spaced from the narrow face of the permanent magnet 2 to the extent that an appreciable air gap is produced which would permit a noticeable stray flux.

The permanent magnet 2 supplies a permanent magnetic bias flux dz, which is closed via the pole pieces 4 and 6, the magnetic yoke 8 and the field plate 10. The magnetic flux 4),, shifts the operating point on the characteristic of the field plate 10 from the basic resistance value to the steep part of said characteristic and thereby produces a magnetic bias of said field plate. The control flux (I), of an external control field is superimposed upon the magnetic flux The external control' field is picked up by the galvanomagnetic resistance device of the invention and is generally not only to be measured, but is also to be converted into an electrical quantity.

The control flux 4;, penetrates the upper pole piece 4, the field plate 10 and at least part of the magnetic yoke 8, which may also function as the base plate of the device. The field plate 10 may be affixed to the magnetic yoke 8 via electrical insulation. In this arrangement, only a negligibly small part of the control flux 4a, penetrates the lower pole piece 6 of the galvanomagnetic resistance device, due to the higher magnetic resistance of such path. The essential parts of the configuration are thus the magnet 2, the pole piece 4 and the field plate 10. x

The permanent magnet 2 may preferably comprise an oxide magnet of low permeability and correspondingly high magnetic resistance. A magnet of such type may be manufactured with a very small thickness of a few tenths of a millimeter. Rare earth cobalt permanent magnetic material is well suited for the galvanomagnetic resistance device of the invention.

The decoupling effect may be further enhanced in the embodiment of FIG. 2 by maintaining the crosssection of the pole piece 6, which is practically not penetrated by the control field 4),, smaller than the crosssection of the pole piece 4, which is penetrated by said control field. The cross-section of the pole piece 6 may preferably be formed so that it is at least approximately saturated by the biasing flux d), of the magnet 2. The correspondingly higher magnetic resistance of the pole piece 6 then counteracts the splitting of the control field In a similar manner, the cross-section of the magnetic yoke 8 may also be maintained small, if desired. The magnetic yoke 8 may then be made by bending one end of the pole piece 6, so that said magnetic yoke then comprises a portion of said pole piece. The magnetic bias of the field plate It) is correspondingly increased due to the lack of an air gap between the pole piece 6 and the yoke 8.

A particularly advantageous embodiment of the galvanomagnetic resistance device of the invention includes the feature that the narrow faces of the permanent magnet 2, which are not in contact with the magnetic yoke 8, protrude somewhat beyond the ends of the pole pieces 4 and 6. The stray field at the narrow faces of the pole pieces 4 and 6 is then forced to follow a path around the narrow faces of the permanent magnet 2, as shown in FIG. 3.

FIG. 3 illustrates one end of the galvanomagnetic resistance device in which the narrow faces at one end of the magnet 2 extend beyond the pole pieces 4 and 6. In FIG. 3, the field lines of the magnet 2 are opposed to the initial stray flux of the pole pieces 4 and 6 indicated by broken lines. The stray flux is therefore considerably reduced in the embodiment of FIG. 3 and a substantial part of said stray flux is thus utilized since such part then passes through the air gap in which the field plate It] is positioned.

In the embodiment of FIG. 4, the magnetic yoke functions as the base plate and supports the field plate 10 which may preferably have meander shape. The active part of the meander pattern of the field plate lltl is covered by a narrow face of the pole piece 4, so that magnetic lines of force emanating from suchnarrow face penetrate said field plate. The second pole piece 6 contacts the opposite flat face of the magnet 2. The cross-section of the second pole piece 6 may be smaller than that of the first pole piece 4.

Soldering tabs 12 and 13 for electrical leads 15 and 16 are provided at the ends of the meander pattern which does not belong to the active part of the field plate ill). The electrical leads 15 and 16 are preferably flat and may be held on the base plate 8 by the magnet 2. The leads l5 and 16 thus pass beneath the permanent magnet 2.

The magnet 2 may, for example, be about 0.8 mm thick and may have a length or height of approximately 4 mm and a width of approximately 4 mm. The thickness of the pole piece 4 is then generally selected in accordance with the width of the field plate 10 to be covered and may, for example, also be approximately 0.8 mm. The thickness of the second pole piece 6 is approximately 0.2 to 0.4 mm, and is thus considerably less than that of the first pole piece 4. The same thickness is sufficient for the base plate or yoke 8, especially if the magnetic yoke effect is generally further amplified by a collector plate which functions as a magnetic antenna for the stray field. If the galvanomagnetic resistance device is to be operated without collector plates (FIGS. 1 to 5), the magnetic yoke 8 may have a suitable thickness of approximately 0.4 mm.

As is well known, the induction in the biasing circuit of the magnet 2 is higher, the smaller the air gap containing the field plate 10. The induction of the biasing circuit thus varies inversely with the air gap. The field plate lit) may therefore preferably be provided without support in the galvanomagnetic resistance device of the invention and may be disposed directly on the magnetic yoke 8 which functions as the base plate, or on the narrow face of the pole piece 4 which defines the boundary of the air gap, provided only with sufficient electrical insulation.

When the field plate Ml has a thickness of at least 10 microns, for example, an insulating layer having a thickness of at least 15 microns, a cement layer 10 microns thick for affixing said field plate, and an upper covering of the field plate having a thickness of approximately 15 microns for protecting said field plate against the pole piece a, the total length of the air gap is only about 50 microns. If the base plate 8 and the pole piece 6 are made from one piece of material, the additional air gap between said base plate and said pole piece may be eliminated, as shown in FIG. 2, and the sensitivity of the device is correspondingly increased.

The electrical leads l5 and 116 of the field plate 10, which pass beneath the magnet 2 and along one flat face of said magnet, as shown in the embodiment of FIG. 4, may be affixed to the magnet and are held in a stable position by said magnet. This considerably increases the mechanical stability of the field plate 10, although it is only a few microns thick. A tensile force on the leads l5 and 16 may have no effect on the contacts at the field plate 36.

The second air gap between the pole piece 6 and the yoke 8 in the embodiments of FIGS. l and 4 has an advantageous effect of drawing the control field 4), away from said pole piece. This results in an increase in the useful flux in the field plate Elli. 0n the other hand, the second air gap between the pole piece 6 and the yoke 8 has the disadvantage of an increased resistance for the biasing circuit flux This results in reduced efficiency of the galvanomagnetic resistance device of these embodiments.

It has been found that the aforedescribed contradictory requirements may be taken into account in a particular configuration of the galvanomagnetic resistance device of our invention. In the embodiment of FIG. 5, the pole piece 6 may be so dimensioned that the biasing flux (11,, which leaves a contact area F, indicated by broken dots and lines in FIG. 5, of said pole piece and the magnet 2, and which adds up over the length or height of said pole piece, results in at least approximate saturation of the transition surface f, indicated by broken lines, to the yoke 8. This results in an increased magnetic resistance for the control field :1), and therefore a better deflection of the control flux (is, to the air gap containing the field plate ill. The decoupling of the biasing flux 4),, and the control flux qt, is thus achieved by magnetic saturation of part of the permanent magnet circuit and by said control flux taking the path of least resistance, which is via the pole piece a and the air gap containing the field plate iii).

A particularly advantageous embodiment of the galvanomagnetic resistance device of our invention is provided by making the pole piece 6 and the yoke 8 of one piece of material and by providing a desired area ratio F f (FIG. by reducing the cross-section in the transition part between said pole piece and said yoke. This may be accomplished, for example, by the indentation in the pole piece 6 of the embodiment of FIG. 5. The area ratio isapproximately selected as preferably at least 5 2 1. More particularly, the area ratio is selected as preferably approximately 1. In such embodiment, the increased resistance due to the air gap is eliminated but the deflection of the control flux (12,,

remains.

The stray flux at the narrow faces of the pole pieces 4 and 6 is also reduced by the flux of the part of the magnet 2 which protrudes laterally beyond said pole pieces. A substantial part of such stray flux is converted into useful flux by displacement toward the air gap.

FIGS. 611,612, 60 and 6d illustrate still another particularly advantageous embodiment of the galvanomagnetic resistance device of the invention. The embodiment of FIGS. 6a, 6b, 6c and 6d includes collector plates for the external control field (1),. The collector plates are known as such, but, in the embodiment of FIGS. 6a, 6b, 6c and 6d, are specifically adapted and function as magnetic sensing antennae.

In FIG. 6a, the control field (1),, extends transversely to the magnetic axis of the magnet 2 and therefore extends in longitudinal directions of the galvanomagnetic resistance device. The external control field is captured by a collector plate 20. The collector plate has one leg or end affixed to the pole piece 41 and a free leg or end projecting beyond the galvanomagnetic resistance device toward the control field (1),, and in at least approximately a direction of said control field. The free end or leg of the collector plate 20 extends beyond the end of thepole piece 4 opposite that adjacent the field plate 110.

In FIG. 6a, another collector plate 21 has a leg affixed to the yoke s. The collector plate 21 is bent at a predetermined angle which, in FIG. 6a, is a right angle. The free leg of the collector plate 2H extends away from the galvanomagnetic resistance device in approximately a longitudinal direction of said device and thereforein a direction of the control field The free leg of the collector plate 21 thus extends away from the yoke 3.

The thickness of the magnetic antennae or collector plates 20 and 21 depends upon the maximum magnitude of the control field (1),. The thickness is preferably selected so that no saturation occurs in the collector plates 20 and 21. In the galvanomagnetic resistance device of the embodiment of FIG. 4, for example, the thickness of the collector plates may, for example, be approximately 0.2 mm. The collector plates in such embodiment may have a width, which generally depends upon the width of the magnetic yoke 8 and the width of the pole piece 4, of approximately 2 mm.

The end of the collector plate 20 is preferably spaced a predetermined distance from the air gap containing the field plate It), so that the stray flux between the collector plates 29 and 2B, which does not penetrate the air gap and thus does not penetrate the field plate 10, is kept negligibly small. The modification of FIG. 6a is suitable for picking up a homogeneous control field the direction of which is indicated by an arrow in FIG. 6a.

The modification of FIG. 6a is also suitable for measuring a curved magnetic field which enters the collector plate 20 perpendicularly to the position of said collector plate from above, penetrates the pole piece 4, the field plate Ill and the yoke 8, and leaves, upward, via the collector plate 21. A curved magnetic field of this type may be provided, for example, by a magnet having poles which are positioned side by side at a predetermined distance which is smaller than the overall extent of the magnetic sensing antennae 20 and 21. Thus, for example, a horseshoe magnet may be utilized to provide the curved'magnetic field.

The modification of FIG. 6b is provided, for example, for measuring a control flux or field d), extending in a direction of the magnetic axis of the magnet 2. A first collector plate or magnetic sensing antenna 22 is affixed at one leg to the pole piece 4. The collector plate 22 is bent at an angle so that its free leg extends away from the galvanomagnetic resistance device and in a direction against the control flux The leg of the collector plate 22 which is affixed to the pole piece 4 may be spaced a predetermined distance from the field plate 10 in order to keep the stray field between said leg and the end of a second collector plate or magnetic sensing antenna 23 small.

The second collector plate 23 has one end or leg affixed to the magnetic yoke 8 and a free end or leg extending away from the galvanomagnetic resistance device, and therefore away from said yoke in a direction of the control field 4, The second collector plate 23 may be bevelled to a certain extent at its leg affixed to the yoke 8 in order to reduce the stray flux.

The modification of FIG. 6c is provided in order to pick up a control field 4:, having a shape indicated by broken dots and lines. The external control field 4:, may, for example, be only the relatively weak stray flux of a magnetic field. A first collector plate or magnetic sensing antenna 2a is bent at a predetermined angle, as is a second collector plate or magnetic sensing antenna 25..

Gne leg of the first collector plate 24 is affixed to the pole piece a. The free leg of the first collector plate 24 extends away from the galvanomagnetic resistance device and in a direction of the control field One leg of the second collector plate 25 is affixed to the yoke 8. The free leg of the second collector plate Z extends away from the galvanomagnetic resistance device and in a direction against the control field The modification of FIG. 6c permits the detection of very weak fields such as, for example, very low fringe and stray fields in the order of a few mT.

In some circumstances it is desirable to bend each of the first and second collector plates at an angle different from in a manner shown in the modification of FIG. 6d. In the modification of FIG. dd, a first collector plate or magnetic sensing antenna 26 has one end affixed to the magnetic yoke 8 and a free end extending away from the galvanomagnetic resistance device in a direction of the external control field gb, to be picked up. A second collector plate or magnetic sensing antenna 27 has one end affixed to the pole piece 3 and a free end extending away from the galvanomagnetic resistance device in a direction against the external control field 4),.

The modification of FIG. dd is particularly well suited for picking up at least approximately homogeneous magnetic fields. Each of the first and second collector plates 26 and 27 is bent at an angle a. The angle a is so selected that the magnetic resistance which the control flux (b, meets in the galvanomagnetic resistance device in the path through the pole piece 4, the field plate and the magnetic yoke 8, becomes as small as possible.

An indication of the capability of the galvanomagnetic resistance device of the invention is its field sensitivity, that is, the change in resistance of the field plate in a homogeneous control field (1a,. The field sensitivity is represented as the slope S of the characteristic in which the resistance is plotted against the induction, for a given value of the induction B. The field sensitivity is thus designated 8;, and is indicated in ohms per millitesla.

When the magnet 2 of the galvanomagnetic resistance device is an oxide magnet of strontium ferrite, the basic resistance of field plate 10 is 40 ohms, the air gap containing the field plate is 60 microns, the magnetic bias induction is approximately 0.56 Tesla and the power loss at the operating point of the field plate is 100 milliwatts, the galvanomagnetic resistance device of our invention, without collector plates, having a field plate resistance at an operating point of R, of 190 ohms, has a field sensitivity 8,, of approximately 2.5 ohms per millitesla.

When collector plates or magnetic sensing antennae are utilized, as shown in FIGS. 6a, 6b, 6c and 6d, the field sensitivity can be increased considerably. When the collector plates comprise soft iron having a width of2 mm, a thickness of 0.2 mm and a length of approximately 10 mm at the pole piece and approximately 8 mm at the yoke, the field plate resistance at the operating point R, being 185 ohms, the field sensitivity of the galvanomagnetic resistance device is increased to more than 1 1 ohms per millitesla. When the length of the collector plates is increased to 20 and 18 mm, respec-' tively, at a field plate resistance at the operating point of R, of 173 ohms, the field sensitivity of the galvanomagnetic resistance device of the invention may be increased to 16 ohms per millitesla.

While the invention has been described by means of specific examples and in specificembodiments, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

We claim:

1. A magnetic field-dependent resistance device for sensing the magnitude and direction of an external magnetic control flux, said device comprising a magnetic circuit including a permanent magnet of slight permeability and high magnetic resistance having poles with pole ends and pole faces, a length which is small in the direction of its magnetic axis relative to the area of its pole face, narrow faces and flat faces, a yoke of ferromagnetic material contacting a narrow face of the permanent magnet with a minimal spacing, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces adjacent the pole ends of the poles of the magnet and connected to each other via the yoke and the field plate, one of the pole pieces having an end defining an air gap with the yoke and the field plate being in the air gap, whereby the control flux penetrates the yoke and the one of the pole pieces.

2. A magnetic field-dependent resistance device as claimed in claim 1, wherein the yoke comprises a part of the other of the pole pieces bent at approximately right angles to said other of the pole pieces, said other of said pole pieces being free from the control field.

3. A magnetic field-dependent resistance device as claimed in claim 1, wherein each of the pole pieces contacts a corresponding flat face of the magnet and the area of the pole pieces is smaller than the area of the adjoining fiat faces of the magnet.-

4. A magnetic field-dependent resistance device as claimed in claim 1, wherein the cross-section of the other of the pole pieces is smaller than the crosssection of the one of the pole pieces in directions of the magnetic axis of the magnet.

5. A magnetic field-dependent resistance device as claimed in claim 1, wherein the magnet comprises an oxide magnet.

6. A magnetic field-dependent resistance device as claimed in claim 1, wherein the magnet comprises a magnet containing cobalt and at least one of the rare earths.

7. A magnetic field-dependent resistance device as claimed in claim 1, further comprising at least one collector plate affixed to one of the pole pieces for capturing the control flux.

8. A magnetic field-dependent resistance device as claimed in claim 3, wherein one end of the one of the pole pieces is penetrated by the control fiux and the field plate is positioned between said one end of said one of the pole pieces and the yoke, and wherein the field plate has electrical leads passing between the magnet and the yoke.

9. A magnetic field-dependent resistance device as claimed in claim 7, wherein the collector plate has a leg affixed to one of the pole pieces and a free leg extending away from the device and having a length approximately three times the length of each of the pole pieces.

10. A magnetic field-dependent resistance device as claimed in claim 7, wherein the collector plate has a leg affixed to one of the pole pieces and a free leg extending away from the device and having a length approximately five times the length of each of the pole pieces.

111.. A magnetic field-dependent resistance device as claimed in claim 7, wherein the device senses an external field substantially perpendicular to the axis of the magnet, and wherein the collector plate has a leg affixed to the one of the pole pieces and a free leg extending away from the device and approximately aligned in a direction of the external field and projecting beyond the end of the one of the pole pieces opposite the field plate.

12. A magnetic field-dependent resistance device as claimed in claim 7, wherein the device senses an external magnetic field extending approximately in a direction of the axis of the magnet, and wherein the collector plate has a leg affixed to the one of the pole pieces and a free leg extending away from the device and approximately aligned in a direction of the external field.

13. A magnetic field-dependent resistance device as claimed in claim 7, further comprising another collector plate affixed to the yoke, each of the collector plates being bent at an angle, theone of the collector plates having a free leg extending away from the device in a direction of the control flux, and the other of the collector plates having a free leg extending away from the device in a direction against the control flux.

14. A magnetic field-dependent resistance device as claimed in claim 11, further comprising another collector plate having a leg affixed to the yoke and a free leg 11 extending away from the device and approximately aligned in a direction of the external field.

15. A magnetic field-dependent resistance device as claimed in claim 11, further comprising another collector plate affixed to the yoke and extending away from the device and approximately aligned in a direction of the external field.

16. A magnetic field-dependent resistance device as claimed in claim 13, wherein the device senses an external field extending in a direction inclined to the magneticaxis of the magnet, and wherein the free legs of thecollector plates extend at apredetermined angle to the magnetic axis of the magnet.

17. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate,--and ferromagnetic pole pieces incontact with the poles of the magnet and connected'to each other via the yoke and the field plate, one of said pole pieces having a cross section which is smallerthan the'crosssection of the other pole pieces so that-said one pole-piece is at least approximately saturated by the bias flux-of the magnet.

18. A galvanomagnetic resistance device as claimed in claim 17, wherein the pole pieces contact the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the area of the flat face of the magnet contacting the other of the pole pieces is substantially greater than the cross-section of said otherof said pole pieces at its end facing the yoke. I i A v 19. A galvanomagnetic resistanceas claimed in claim 17, wherein the pole pieces contact the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the'pole pieces being'free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is at least approximately l.

' 20. A galvanomagnetic resistance as claimed in claim 17, wherein the pole pieces contact the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is approximately '10 l.

21. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux,'a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, whereby part of magnetic circuit is at least approximately saturated by the bias flux of the magnet, said pole pieces contacting the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other ofthe pole pieces having an end facing the yoke, and wherein the area of the flat face of, the magnet contacting the other of the pole pieces is substantially greater than the cross-section of said other of said pole pieces at its end facing the yoke.

22. A galvanomagnetic resistance device as claimed in claim 21, wherein the other of the pole pieces is constricted in cross-section at its end facing the yoke.

23. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, whereby part of the magnetic circuit is at least approximately saturated by the bias flux of the magnet, said pole pieces contacting the flat faces of the magnet and the control .field penetratesthe yoke and one of the pole pieces, the other of the pole pieces being freefrom the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is at least approximately '5 24. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, whereby part of the magnetic circuit is at least approximately saturated by the bias flux of the magnet, said pole pieces contacting the flat. faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an plate along with the yoke and the one of said pole pieces. 

1. A magnetic fIeld-dependent resistance device for sensing the magnitude and direction of an external magnetic control flux, said device comprising a magnetic circuit including a permanent magnet of slight permeability and high magnetic resistance having poles with pole ends and pole faces, a length which is small in the direction of its magnetic axis relative to the area of its pole face, narrow faces and flat faces, a yoke of ferromagnetic material contacting a narrow face of the permanent magnet with a minimal spacing, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces adjacent the pole ends of the poles of the magnet and connected to each other via the yoke and the field plate, one of the pole pieces having an end defining an air gap with the yoke and the field plate being in the air gap, whereby the control flux penetrates the yoke and the one of the pole pieces.
 2. A magnetic field-dependent resistance device as claimed in claim 1, wherein the yoke comprises a part of the other of the pole pieces bent at approximately right angles to said other of the pole pieces, said other of said pole pieces being free from the control field.
 3. A magnetic field-dependent resistance device as claimed in claim 1, wherein each of the pole pieces contacts a corresponding flat face of the magnet and the area of the pole pieces is smaller than the area of the adjoining flat faces of the magnet.
 4. A magnetic field-dependent resistance device as claimed in claim 1, wherein the cross-section of the other of the pole pieces is smaller than the cross-section of the one of the pole pieces in directions of the magnetic axis of the magnet.
 5. A magnetic field-dependent resistance device as claimed in claim 1, wherein the magnet comprises an oxide magnet.
 6. A magnetic field-dependent resistance device as claimed in claim 1, wherein the magnet comprises a magnet containing cobalt and at least one of the rare earths.
 7. A magnetic field-dependent resistance device as claimed in claim 1, further comprising at least one collector plate affixed to one of the pole pieces for capturing the control flux.
 8. A magnetic field-dependent resistance device as claimed in claim 3, wherein one end of the one of the pole pieces is penetrated by the control flux and the field plate is positioned between said one end of said one of the pole pieces and the yoke, and wherein the field plate has electrical leads passing between the magnet and the yoke.
 9. A magnetic field-dependent resistance device as claimed in claim 7, wherein the collector plate has a leg affixed to one of the pole pieces and a free leg extending away from the device and having a length approximately three times the length of each of the pole pieces.
 10. A magnetic field-dependent resistance device as claimed in claim 7, wherein the collector plate has a leg affixed to one of the pole pieces and a free leg extending away from the device and having a length approximately five times the length of each of the pole pieces.
 11. A magnetic field-dependent resistance device as claimed in claim 7, wherein the device senses an external field substantially perpendicular to the axis of the magnet, and wherein the collector plate has a leg affixed to the one of the pole pieces and a free leg extending away from the device and approximately aligned in a direction of the external field and projecting beyond the end of the one of the pole pieces opposite the field plate.
 12. A magnetic field-dependent resistance device as claimed in claim 7, wherein the device senses an external magnetic field extending approximately in a direction of the axis of the magnet, and wherein the collector plate has a leg affixed to the one of the pole pieces and a free leg extending away from the device and approximately aligned in a direction of the external field.
 13. A magnetic field-dependent resistance device as claimed in claim 7, further comprising another collector plate affixed to the yoke, each of the collector plaTes being bent at an angle, the one of the collector plates having a free leg extending away from the device in a direction of the control flux, and the other of the collector plates having a free leg extending away from the device in a direction against the control flux.
 14. A magnetic field-dependent resistance device as claimed in claim 11, further comprising another collector plate having a leg affixed to the yoke and a free leg extending away from the device and approximately aligned in a direction of the external field.
 15. A magnetic field-dependent resistance device as claimed in claim 11, further comprising another collector plate affixed to the yoke and extending away from the device and approximately aligned in a direction of the external field.
 16. A magnetic field-dependent resistance device as claimed in claim 13, wherein the device senses an external field extending in a direction inclined to the magnetic axis of the magnet, and wherein the free legs of the collector plates extend at a predetermined angle to the magnetic axis of the magnet.
 17. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, one of said pole pieces having a cross section which is smaller than the cross section of the other pole pieces so that said one pole piece is at least approximately saturated by the bias flux of the magnet.
 18. A galvanomagnetic resistance device as claimed in claim 17, wherein the pole pieces contact the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the area of the flat face of the magnet contacting the other of the pole pieces is substantially greater than the cross-section of said other of said pole pieces at its end facing the yoke.
 19. A galvanomagnetic resistance as claimed in claim 17, wherein the pole pieces contact the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is at least approximately 5 :
 1. 20. A galvanomagnetic resistance as claimed in claim 17, wherein the pole pieces contact the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is approximately 10 :
 1. 21. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, whereby part of magnetic circuit is at least approximately saturated by the bias flux of the magnet, said pole pieces contacting the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the area of the flat face of the magnet contacting the other of the pole pieces is substantially greater than the cross-section of said other of said pole pieces at its end facing the yoke.
 22. A galvanomagnetic resistance device as claimed in claim 21, wherein the other of the pole pieces is constricted in cross-section at its end facing the yoke.
 23. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, whereby part of the magnetic circuit is at least approximately saturated by the bias flux of the magnet, said pole pieces contacting the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is at least approximately 5 :
 1. 24. A galvanomagnetic resistance device for sensing the magnitude and direction of an external magnetic control field, said device comprising a magnetic circuit including a permanent magnet having poles, narrow faces and flat faces and producing a bias flux, a yoke of ferromagnetic material, a magnetic field-dependent resistance comprising a field plate, and ferromagnetic pole pieces in contact with the poles of the magnet and connected to each other via the yoke and the field plate, whereby part of the magnetic circuit is at least approximately saturated by the bias flux of the magnet, said pole pieces contacting the flat faces of the magnet and the control field penetrates the yoke and one of the pole pieces, the other of the pole pieces being free from the control field, the other of the pole pieces having an end facing the yoke, and wherein the ratio of the area of contact of the other of the pole pieces and the magnet to the cross-section of the end of the other of the pole pieces facing the yoke is approximately 10 :
 1. 25. A galvanomagnetic resistance device according to claim 1 wherein the control flux penetrates the field plate along with the yoke and the one of said pole pieces. 